1. Field of the Invention
The present invention relates to the technology of the touch control field, and more particularly to a sensing system and a method for obtaining a position of a pointer.
2. Description of the Related Art
FIG. 1 is a three dimensional view of a conventional sensing system. Referring to FIG. 1, the sensing system 100 is configured for sensing a position of a pointer 102. The sensing system 100 comprises a reflective mirror 104, light-reflecting elements 106 and 108, an image sensor 110 and a processing circuit 112. The reflective mirror 104, the light-reflecting elements 106 and 108, and the image sensor 110 are all disposed on a same plane 114. The plane 114 may be a whiteboard. In addition, a rectangular area indicated by a label 116 is used as a sensing area of the sensing system 100.
The light-reflecting elements 106 and 108 are both configured for reflecting light to the sensing area 116, and the reflective mirror 104 is configured for generating a mirror image of the sensing area 116. The reflective mirror 104 may be a plane mirror having a mirror surface 118, and the mirror surface 118 faces towards the sensing area 116. The image sensor 110 is disposed at a corner of the sensing area 116, and has a sensing range covering all of the sensing area 116. The processing circuit 112 is electrically coupled to the image sensor 110 for calculating the position of the point 102 according to an image sensed by the image sensor 110.
FIG. 2 is an explanatory view for describing an operation mode of the sensing system 100. As shown in FIG. 2, a portion below a broken line 202 briefly illustrates a part of the sensing system 100, which can be mirrored by the mirror surface 118; and a portion above the broken line 202 is a mirror image of the part of the sensing system 100, which is generated by the mirror surface 118 mirroring the part of the sensing system 100. In FIG. 2, an object indicated by a label 106′ is a mirror image of the light-reflecting element 106, an object indicated by a label 108′ is a mirror image of the light-reflecting element 108, an object indicated by a label 110′ is a mirror image of the image sensor 110, an area indicated by a label 116′ is a mirror image of the sensing area 116, and an object indicated by a label 102′ is a mirror image of the pointer 102. Thus the image sensor 110 can sense the pointer 102 along a sensing route 204, and also can sense the mirror image 102′ of the pointer 102 along a sensing route 206.
FIG. 3 is a schematic view of the image sensed by the image sensor 110 as shown in FIG. 2. In FIG. 3, a label 300 represents an image-sensing window of the image sensor 110. A diagonal area indicated by a label 302 is a bright zone with high luminance formed on the image via reflecting the light by the light-reflecting element 106 and the reflective mirror 104. The bright zone 302 is a main sensing area. A label 304 represents a dark mark caused by the pointer 102, and a label 306 represents another dark mark caused by the mirror image 102′ of the pointer 102. Therefore, the processing circuit 112 can further calculate the position of the pointer 102 according to positions of the dark marks 304 and 306 in the image-sensing window 300. A relevant calculating method thereof is disclosed in the U.S. patent application Ser. No. 12/249,222 which claimed the priority of Taiwan Patent application No. 097126033.
However, the sensing system 100 has a disadvantage, which will be described in FIG. 4. FIG. 4 is another explanatory view for describing another operation method of the sensing system 100. As shown in FIG. 4, when the pointer 102 approaches a periphery 192 of the sensing area 116, although the image sensor 110 still can sense the pointer 102 along a sensing route 402 and sense the mirror image 102′ of the pointer 102 along a sensing route 404, the image sensed by the image sensor 110 may only have a single dark mark appeared therein, which will be described in FIG. 5, since the sensing routes 402 and 404 are too close.
FIG. 5 is a schematic view of the image sensed by the image sensor 110 as shown in FIG. 4. As shown in FIG. 5, the dark mark indicated by a label 502 cannot be determined to be the dark mark caused by the pointer 102 or the dark mark caused by the mirror image 102′ of the pointer 102. Thus the sensing system 100 cannot calculate the position of the pointer 102.